Acute leukemia is a rapidly progressive malignant disease of the bone marrow and blood that results in the accumulation of immature, functionless cells, called blast cells, in the marrow and blood. The accumulation of blast cells in the marrow blocks normal blood cell development. As a result, red cells, white cells and platelets are not produced in sufficient numbers. When the disease originates in a marrow lymphocyte progenitor cell, it results in acute lymphoblastic leukemia (ALL) and when the disease originates in a myeloid progenitor, it results in acute myelogenous leukemia (AML).
ALL is a rapidly progressive cancer that starts by the malignant transformation of a marrow lymphocyte. ALL is the most common type of childhood leukemia, with 3,000 new cases per year in all age groups. The transformed, now malignant, cell multiplies and accumulates in the marrow as leukemic lymphoblasts. The lymphoblasts block normal blood cell-formation in the marrow, resulting in insufficient production of red cells, white cells and platelets.
High-grade lymphomas, also known as aggressive lymphoma, include several subtypes of lymphoma that progress relatively rapidly if untreated. These subtypes include, e.g., AIDS-associated lymphoma, anaplastic large cell lymphoma, Burkitt's lymphoma, diffuse large cell lymphoma, immunoblastic lymphoma, lymphoblastic lymphoma and small noncleaved cell lymphomas. Compared to diffuse large B-cell lymphomas, high-grade lymphomas behave more aggressively, require more intensive chemotherapy, and occur more often in children. Because rapidly dividing cells are more sensitive to anti-cancer agents and because the young patients usually lack other health problems, some of these lymphomas show a dramatic response to therapy. Acute lymphoblastic leukemia and high-grade lymphoma are the most common leukemias and lymphomas in children. These diseases are, for the most part, polyclonal, suggesting that only a few genetic changes are sufficient to induce malignancy.
ALL-1, also termed MLL has been cloned from chromosome band 11q23, recurrent site involved in multiple chromosome abnormalities associated with both acute lymphoblastic (ALL) and acute myeloblastic (AML) leukemia (1, 2). The chromosome translocation results in the fusion of the ALL1 gene with one of more than 50 different partner genes and the production of leukemogenic proteins composed of the N-terminal All1 sequence and a portion of the partner protein encoded by the segment of the gene positioned 3′ to the breakpoint (ibid). The most prevalent ALL1 rearrangement in ALL is the ALL1/AF4 chimeric gene resulting from the t(4;11) chromosome translocation. This rearrangement is associated with very poor prognosis in infants and adults (3). The molecular pathways deregulated by the All1 fusion protein, which bring about the aggressiveness of the disease are still largely unknown.
miRNAs are short 20-22 nucleotide RNA that negatively regulate the gene expression at the post-transcriptional level by base pairing to the 3′ untranslated region of target messenger RNAs. More than 400 miRNAs have been identified in human and they are evolutionarily conserved. It has been shown that miRNAs regulate various physiological and pathological pathways such as cell differentiation, cell proliferation and tumorigenesis (reviewed in 4). Extensive studies to determine expression profile of miRNAs in human cancer has revealed cell-type specific miRNA fingerprint found in B cell chronic lymphocytic leukemia (B-CLL), breast cancer, colon cancer, gastric cancer, glioblastoma, hepatocellular carcinoma, papillary thyroid cancer, and endocrine pancreatic tumors (reviewed in 5).
Calin et al. showed that although miRNA genes represent only 1% of the mammalian genome, more than 50% of miRNA genes are located within region associated with amplification, deletion and translocation in cancer (6). Such somatic changes of miRNA genes definitively attribute to the specific expression pattern found in cancer. Additional factors, which attribute to the cancer specific deregulation of miRNAs, are unknown, although the most obvious candidate is transcriptional control. Other possibility is that miRNA maturation is such factor. Micro RNA biogenesis begins with a primary transcript, termed pri-miRNA, which is generated by RNA polymerase II (review in 7). Within the pri-miRNA, the miRNA itself is contained within a ˜60-80 nucleotide that can fold back on itself to form a stem-loop hairpin structure. This hairpin structure is recognized and excised from pri-miRNA by the microprocessor complex composed of nuclear RNase III enzyme, Drosha and its binding partner DGCR8. The excised miRNA hairpin, referred to as pre-miRNA, is transported to the cytoplasm in association with RAN-GTP and Exportin 5, where it is further processed by a second RNase III enzyme, Dicer, which releases a 22 nucleotide mature duplex RNA with 5′ phosphate and 2-nucleotide 3′ overhang. The antisense RNA strand is incorporated into the RISC complex, which target it to mRNA(s) by base-pairing and consequently interfere with translation of the mRNA or cleave it. In principle, any step during this maturation process could affect miRNA production.
Consequently, there is a need for agents that regulate gene expression via the mechanisms mediated by small non-coding RNAs. Identification of oligomeric compounds that can increase or decrease gene expression or activity by modulating the levels of miRNA in a cell is therefore desirable.
The present invention therefore provides oligomeric compounds and methods useful for modulating the levels, expression, or processing of pri-miRNAs, including those relying on mechanisms of action such as RNA interference and dsRNA enzymes, as well as antisense and non-antisense mechanisms. One having skill in the art, once armed with this disclosure will be able, without undue experimentation, to identify compounds, compositions and methods for these uses.